The Teenage Years
by SmartFangirlCookie
Summary: Being a teenager has its challenges, but Phineas and Ferb are always ready to take them on. Romance, growing up, and the drama that comes with it are playing bigger and bigger roles in Phineas and Ferb's lives. Can they rise up to the challenge? Pairings: Phineas/Isabella, Ferb/Vanessa, Candace/Jeremy (and probably more!) It's my first fanfiction, so please read and enjoy!
1. Chapter 1

**Hey guys! This is my first fanfic, so I hope you enjoy it! I'll try to post regularly, maybe every week or so! If you want updates, you can check out my tumblr! (Hint: it's the same as my username!) I hope to include other aspects of their life other than romance. I want this to be a fanfic that gives you an idea of where the Phineas and Ferb characters are at 15 (this includes Doofensmirtz and Perry the Platypus. Obviously they're not 15, but Phineas and Ferb are.) Please rate and comment! I want any input you guys have!**

 **Isabella POV**

Isabella loved going to that familiar backyard with the gigantic oak tree. The two boys who inhabited it (well, one more than the other) made it even better, what with their incredible exploits every day of the summer. It was even better, now that she hadn't been able to visit it for an entire week because of camporee. It seemed like distance made it even more precious. The backyard wasn't the only thing that she missed in her week of absence. A certain ginger-haired boy loomed in her mind. Sure, he never seemed to notice her flirting (and it was very obvious), but somehow he still managed to make it impossible to give up on him. It was something about the fiery red hair falling into his ocean blue eyes and his adorable smiles and his inventiveness and his adorable optimism and-

And there she went into Phineas-land. It was exactly why she couldn't just _give up_ on him. It wasn't her little crumb cake's fault that he was just so adorable and all kinds of wonderfulness in one person.

It was unfair.

She had to mentally prepare herself to see him. She was currently rehearsing her catchphrase in her head. _Whatcha doin'. What_ cha _doin'._ What _cha_ do _in'. Yeah, that was it._

It was go-time.

She unlatched the fence in the same way she had been doing since she was eight.

"Hey, Phineas. What _cha_ doin'?"

She mentally slapped herself. That was _not_ the way she rehearsed. _Oh, he's turning around now. He's_ so _cute. He's opening his mouth. Oh, I'm so glad that he finally got the braces off. He looks so much more adorable. Not that he's not still adorable._

"Hey, Isabella. Ferb and I are just building a life-size replica of the Eiffel Tower out of popsicle sticks," Phineas gestured to the massive wooden structure behind him.

"Oh, wow. It looks _just_ like the real thing! Except, well, you know, made out of popsicle sticks."

"Yeah! That's the idea," he grinned. "You want to see it?"

"Uh, sure!"

Isabella took his open hand. He was suddenly much taller than she was. She remembered when she towered over him (heh!), and she had been worried that it would always be like this, and _of course_ girls can't be the tall ones (well, she didn't believe _that_ anymore).

"-and this is the top!" Phineas turned to her. "So, what do you think?"

Isabella realized that she had zoned out for the entirety of the tour. "Oh, um, it's really cool. Awesome. Great."

"Glad you like it. So, how was camp?"

"Oh, it was great. We sang a lot of songs. Also s'mores. S'mores were good. Uh, Addison sprained her ankle while we were hiking, but that was pretty much it," she responded, scrunching her eyebrows. "Oh, I almost forgot. I got a bunch of patches! And I got some souvenirs for you guys!"

Before Phineas had the chance to respond, a voice called up to him. "How's it going up there, Phineas?"

Isabella narrowed her eyes. "Who's _that_?"

"Oh, that's right! I forgot to tell you. That's Abby," Phineas waved at the brunette at the bottom of the tower. "She just moved here, and she said she wants to join the Fireside Girls! Isn't that cool?"

"Yeah," Isabella frowned. " _Cool._ "

"You should talk to her. She's really nice."

By that point, a girl with chestnut brown hair and luminescent blue eyes had climbed up to where they stood. "How's it going, guys?"

"Hey, Abby," Phineas waved. "This is Isabella."

 _Dang it, she's pretty_.

"Oh, is this the Isabella that I've heard so much about? I'm so glad to meet you!" she exclaimed, pulling Isabella into a hug. "You're so pretty! Phineas, you didn't tell me she was so pretty!"

 _Dang it, she's nice._

Phineas smiled at the floor. "Well, yeah, I guess you could- I mean, not that I didn't- I did tell you a lot about her, though."

Isabella managed a tight-lipped smile. "Thanks. Nice to meet you."

An awkward silence fell upon the group. Desperate to fill the silence, Phineas asked, "So, Abby, you mentioned that you wanted to join the Fireside Girls?"

"Yeah! I've always wanted to join them, but there was never a chapter in my town. I mean, I don't have any experience with the Fireside Girls, but it's better to start late than never, right?"

"Yep," Isabella said, popping the 'p'. "So, where'd _you_ come from?"

"Swampy City. Though for a town that has the word 'city' in the name, it's pretty small," Abby laughed. "You guys go to Danville High, right? I think that's where I'm going in August."

"Are you a sophomore, too?"

"Yeah," Abby smiled. "So, I guess we'll be seeing a lot of each other come two weeks."

"Uh huh."

Phineas looked between the two girls, his head tilted and his eyebrow raised. "Why don't we just go down to Ferb?"

Isabella crossed her arms. "Let's do that."

They reached the ground just in time for Buford and Baljeet to enter the backyard. "What's up, nerds?"

Baljeet trailed behind Buford. "I find 'nerd' to be a very derogatory term. I prefer 'studious individual', or perhaps 'overachieving-'"

"Okay, _nerd_ ," Buford laughed, putting an emphasis on 'nerd'. He smacked his Tuff Gum.

Baljeet looked at the group that emerged from the tower. "Hey, Isabella's back!"

"Hey, guys," she waved to Baljeet. "How's things been going since I've been gone?"

"It's been okay," Baljeet responded. "Have you been shopping for a scientific calculator yet? I think we're going to need it for AP chemistry."

"No, not yet. I will, though."

Abby looked between them. "You guys are taking AP chem? Wow."

"Yeah," Isabella straightened. "Phineas, Baljeet, and I are all taking it this year."

"Impressive."

A pregnant pause filled the conversation. Ferb blinked.

"Isabella, maybe you could introduce Abby to the other Fireside Girls?"

Not taking her eyes off of Abby, Isabella answered, "Sure, Phineas."

Isabella turned on her heel and stomped towards the fence, with Abby on her heels. The boys watched their retreating forms. Ferb murmured, "Well, this is going to be an interesting year."


	2. Chapter 2

**Guys, thank you so much for giving my fanfic a chance! I know I'm not the best, but I'm really glad that it seems like you guys enjoyed it! I said that I would update it every week, and I'll probably update it every Saturday or Sinday. Thank you to all who read it, followed it, and/or reviewed it. I'll try not to let you guys down, and hopefully I'll have time to update it each week. I'll try to work on some of the side plots too, but it _is_** **a romance after all. And without further ado, chapter two!**

Ferb POV

Ferb wished he wasn't such a hopeless romantic. Maybe then he wouldn't feel betrayed.

After all, it wasn't like he was dating her. He had no right to be jealous.

It was just a few days before school started, early in the morning. In the morning was a slight calming breeze, perfect for alone time. Ferb usually walked in the park in the mornings because of this. It was nice, having an early start on the day, and relaxing. At least, it usually was. Today laced him with anxiety.

The very person he hoped to see and hoped to miss happened to be in the park. Ferb saw her before she saw him.

She was perfect. Pure beauty, what with her dark chocolate hair and her stormy gray eyes, suave, five years older, and way out of his league.

He would have waved, had it not been for the dark-haired man with the monobrow that she was walking with. He was her age, handsome (besides the monobrow), and she was clearly smitten with him. There was no way Ferb could even compete. What twenty year old would even be interested in a fifteen year old like him?

So he stayed silent, unnoticed, like he always was. Sometimes the silence bothered him. He noticed how people ignored him and mostly talked with Phineas. Ferb wished he could be noticed, but talking like Phineas did was not in the cards for him.

He would have to find another way.

Just then, a crumpled piece of paper blew by him.

An idea struck him. And it was perfect.

Phineas POV

"Ferb, what do you mean, you're busy? It's the last day of summer! This needs to be perfect! We need to start early, or we might not have enough time for the ice cream slip and slide!"

Ferb had shrugged. "I'll be back."

And then he had left, clutching a basket full of letters and chocolates. Phineas couldn't even imagine what was more important to Ferb than his own brother. This was Phineas' reputation at stake! He and Ferb always build the biggest, bestest project on the last day of summer, and without Ferb, who knows if he could top off last year?

Maybe Phineas was the only one freaking out about the last day of summer. Baljeet had already cancelled on them because of some summer school thing, and Buford with him. Ferb just couldn't opt out of their end of summer extravaganza, too! He wanted to make the biggest, best project he had ever done. He had to make the most of the day. Tomorrow was school, and he just knew he wouldn't have a lot of time for his projects.

Whatever. Phineas could still get started on building the gigantic water guns. He didn't need Ferb, because clearly Ferb didn't need him. Apparently, neither did anyone else.

"Whatcha doing?"

"Hey, Isabella. At least you're someone I can rely on."

Isabella tilted her head. "What happened?"

Phineas sighed. "Ferb had something else to do. I guess it's just you and me for now."

Isabella squealed, then slapped herself. "Sorry. I'm, um, practicing for my drama patch."

Phineas pinched his nose. "Do you know how to use a blowtorch?"

"What?"

Phineas sighed and returned to his work. "Nevermind."

Isabella sat next to him on the grass. Her chocolate brown eyes bored into him. "Phineas, is something bothering you? You seem… stressed."

At that, Phineas blew up. "No, I'm perfectly fine. Peachy. Of course I'm stressed. Ferb isn't here to help me build this gigantic project that the entire neighborhood is expecting to see. Oh, you see Phineas Flynn over there? Yeah, he built that roller coaster through downtown. I bet he's going to build something huge for the last day of summer. It's unrealistic, and I have basically no one to help me, and Buford and Baljeet are going to miss it, and you're literally no help at all."

Phineas instantly regretted the last part. He knew it wasn't true. But judging by Isabella's red-rimmed eyes, she believed it.

"Isabella-"

Standing up, she sniffed, "I think I should go."

He grabbed her wrist. "Isabella, I didn't mean to-"

Isabella stared at the ground. "I want to be alone now. Please."

He had messed up. And he didn't know how to fix it. Phineas held his head in his hands. What to do, what to do…

"Hey, Phineas. Is there a reason that Isabella's sitting in your front lawn?"

He couldn't deal with her right now. He had to find Isabella and apologize. That was what he would do. All he had to do was find her. Wait, did Abby just say…

He darted towards the fence. God, he hoped Isabella would forgive him. What kind of person yells at their friends like that? He was a horrible-

"Ow!"

Phineas tripped over something soft and big, landing on top of them. Who in their right mind would sit on a pathway?

"Sorry," he said, looking into familiar brown eyes that he had known for ages. He took a deep breath. It was now or never. "Isabella, I'm sorry for what I said. I didn't mean it all. I was just really stressed about today and I took it out on you and I know that's no excuse but-"

"Phineas, it's okay."

"No, it's not okay. Izzy, you're one of my best friends, and I don't want to hurt you and-"

Phineas realized then just how close he was to her. If he just leaned a little bit closer-

Where did that thought come from? He pushed it to the back of his mind. It was probably nothing.

He scooted back, sighing. "Look, I'm just really stressed and-"

"I forgive you, Phineas."

Phineas helped Isabella up. "How about we finish these gigantic water guns? I promise to not explode this time."

Isabella smiled. "I'd like that."

Behind them, the sound of footsteps alerted them to another presence. Phineas turned to see-

"Ferb! And Baljeet and Buford!"

"What, you think we would miss out on the last day of summer? No way," Baljeet laughed.

"Aw, you guys!" Phineas hugged his group of friends. "Thanks. I'm glad we get to do this. Together."

Little did they know that they forgot a certain dark haired girl who had heard everything.


	3. Chapter 3

**So I know that I said that I would update on the weekends, but I've decided to update on a weekly basis. Anyways, I want to say thank you to all who have supported this story, which is all of you who have read this far! It really helps to encourage me to keep writing this story, and I promise that I'll finish it! Extra special thanks to those who have followed this story, followed me, favorited this story, and reviewed this story. You guys have been so nice and supportive, and all of the reviews are super positive, so thank you so much for this! I guess you could say this opportunity is a little serendipitous (I'm sorry, I just had to). So for those of you who have read this far, here is chapter three!**

Vanessa inspected the mysterious gift. Someone had left her a hay yellow basket filled to the brim with goodies. Not just _any_ goodies, but her favorite things in the whole world. The music she liked (rock, obviously), the candies that she loved (Red Hots), and the brand of makeup that she wore, all in her favorite color, black. Someone sent this, someone that knew her well. But who would send her this? Could it be Monty, trying to make up after their fight? It was possible, but it wasn't like him to swallow his pride _this_ quickly.

Dr. Doofenshmirtz approached from behind. "What's this?"

"I don't know. A basket, I guess?"

"Who sent you this? Was it Perry the Platypus?" Dr. Doofenshmirtz's eyes darted around. "It could be a trap! From OWCA!"

"Dad-"

"Or-" Doofenshmirtz's eyes narrowed, "Is it a boy? If he hurts you-"

"Dad! It's nothing like that!" Vanessa rolled her eyes. "I don't _know_ what it is. Or who it's from."

"Does it have almond brittle?"

"Dad!"

"I was just wondering! I ran out of my stash, and I really don't feel like going to the store. Ooh! That's _perfect_. No more evil scientist's block for me!"

Doofenshmirtz ran off, laughing evilly. Vanessa shook her head. "How am I going to figure out who sent it?"

Something white caught her eye in the basket. Huh. It was an envelope. How she didn't see the white among the black before, she wasn't sure. Across the front, in bold black letters, read _Vanessa,_ with a little heart. This wasn't Monty's handwriting, for sure. But who else knew her well enough to send it?

Only one thing convinced her that it wasn't Monty.

It was the _letter._

It wasn't that Monty never did romantic gestures like this. It was the _voice_. It felt… different.

 _Why is it that you cause me to feel this way? The tingly feeling, the butterflies, the longing… The girl I watch, but have no courage to speak. The girl who is my everything._

 _Signed,_

 _The boy who says nothing_

It was short, and sweet. She loved it.

Now to find who made it…

OoOoO

"Goodbye, Izzy! Have a good day at school!"

She _wished_.

Isabella had gotten her schedule two days ago, and she only had _one class_ with Phineas. Guess who had almost all their classes with him?

Abby. She had PE, English, and Spanish with him. Which was positively insane. How was it possible? Isabella specifically took AP Chemistry just to be with Phineas, and it was her _only_ class with him.

Which meant that Isabella had to watch Abby walk away with Phineas. Isabella couldn't even _monitor_ her behavior. She suspected that Abby might like Phineas, though yesterday she seemed off when they found her in the backyard. It was certainly interesting.

Abby laughed, brushing against Phineas. Isabella desperately hoped that Phineas didn't notice. Maybe, if he didn't notice, he wouldn't like her. Right?

Isabella sighed. It was going to be a _long_ day.

OoOoO

"Hey," Phineas smiled, sliding into his seat. He was glad that he snagged a seat next to Isabella, though she was currently hunched over her desk, her sleek hair falling in a curtain around her head. He flicked at her hair in an attempt to get her attention. "Izzy? You awake?"

"Huh? Oh, hey, Phineas," Isabella said distractedly. "Sorry. Just writing."

"Whatcha writing?" he imitated her catchphrase, looking over her shoulder. "Is that my name?"

Isabella slammed shut her notebook. "No! I mean-"

Phineas raised his hands. "Sorry, I didn't mean to-"

He was interrupted by the bell. Isabella whispered, "Later."

The door opened behind them, and a disheveled-looking Baljeet stumbled in. The teacher sighed. "Mr. Tjinder, do please come on time tomorrow. I'll let today slide because I'm in a good mood, but this _better_ not happen again."

Baljeet nodded, sliding into the seat Phineas saved for him in front of him. Phineas tapped his shoulder. "Dude, what happened?"

Baljeet ignored him. Phineas raised an eyebrow, turning to look at Isabella, who was already engrossed in the teacher's lecture. He attempted to listen, but to no avail. The entire period, Phineas stared out the window, wishing he could build something. Maybe a… homework machine? No, that was stupid. The teacher apparently didn't notice his lack of attention, because the bell rang before he knew it, signalling lunch.

Phineas gathered his books. "Baljeet, seriously, what happened?"

Baljeet ignored him. "I'm thinking I should join the football team."

"What? No, Baljeet-"

Baljeet left before Phineas could put in another word. Phineas exchanged looks with Isabella.

"That was strange," Isabella remarked. Phineas nodded, stroking his chin. "Uh, anyways, do you want to eat lunch with me? I mean, since we haven't talked _all day_."

"Yeah, sure. Do you want to see if Baljeet is okay, first?"

"I think we should give him some alone time. He didn't look like he wanted to talk."

"Yeah, you're right." Phineas nodded. He leaned over Isabella. " _I can't believe that I almost revealed that I liked-"_

Isabella slapped her book closed. "Don't read over my shoulder! Please."

"Sorry. So what do you like? Potatoes? Sweet peas? Platypuses? Platypi?" Phineas furrowed his eyebrows. "Hmm. What's the plural form of platypus?"

" _Phineas."_

"Okay, I'm sorry. But I'm also we get lunch now?"

Isabella sighed, gathering her things. "Apology accepted."

"So," Phineas said as he walked beside Isabella to the cafeteria. "What's the big deal with the notebook? Are you like a secret spy who's been cataloging my every move because you think I'm an alien?"

"Something like that."

"Because _that_ would be cool." Phineas paused. "Isabella? Are you mad about the notebook? Because I'm really sorry if it's important-"

They reached the cafeteria, and Isabella grabbed a tray. "I'm a little worried about Baljeet. He was late today, and he's _never_ late to school. He hates sports, and now he wants to join the football team? I just don't get it."

Phineas finished grabbing his lunch and paid for it. "You're right. But about the notebook-"

"I'm going to get to the bottom of this. I didn't earn my Detective patch for nothing!"

Phineas and Isabella set their trays on their normal table. "Hey, gang."

Ferb was writing away on a paper, while Buford was busy cracking his knuckles at random times between shoving hordes of food into his mouth. Baljeet and Abby, the latter of which had become sort of a regular, were noticeably absent.

"Where's Baljeet?" asked Isabella.

"Yeah, and Abby, too?"

Beside Phineas, Isabella huffed.

A familiar brunette walked past their table. "Hey, Abby!" Phineas called. Abby looked up and started to their table, though promptly turned around and stomped away when she saw Isabella.

"Uh-" Phineas looked at Isabella. "Abby was initiated into the Fireside Girls, right?"

Isabella frowned. "Yeah. Why?"

Buford piped up, "If it were up to me, it looks like she's mad at you. I should know. I _am_ a bully."

"Me?"

"No, Isabella."

"What?" Isabella's eyes widened. "How could she be mad at _me?_ Buford, I get. But me?"

"Yeah, there's no way anyone could dislike Isabella," Phineas looked at Ferb. "Right?"

Ferb didn't look up. Isabella said, "What do you think I did wrong? Do you think I should try to talk to her?"

Abby was already walking away. It was now or never. Isabella stood up and ran after her, the boys watching her leave.

OoOoO

Isabella was nearly out of breath before she reached Abby in the courtyard. "Abby," she wheezed. "I need- to talk- to you."

The next words that came out of Abby's mouth shook Isabella to her core.

"You like Phineas, don't you?"

OoOoO

No, there was no way Candace would believe it. It just _couldn't_ be possible. Was it wrong?

It couldn't be. It was the only thing that explained everything.

What would she tell Jeremy?


End file.
